Hall effect ferromagnetic random access memory device and its method of manufacture

ABSTRACT

A Hall effect ferromagnetic non-volatile random access memory cell comprising a Hall effect sensor adjacent to a ferromagnetic bit which is surrounded by a drive coil. The coil is electrically connected to a drive circuit, and when provided with an appropriate current creates a residual magnetic field in the ferromagnetic bit, the polarity of which determines the memory status of the cell. The Hall effect sensor is electrically connected via four conductors to a voltage source, ground, and two read sense comparator lines for comparing the voltage output to determine the memory status of the cell. The read and write circuits are arranged in a matrix of bit columns and byte rows. A method for manufacturing said Hall effect ferromagnetic non-volatile random access memory cell.

RELATED APPLICATIONS

This is a Divisional application of pending application Ser. No.09/218,344, filed Dec. 22, 1998 now U.S. Pat. No. 6,140,139 entitledHALL EFFECT FERROMAGNETIC RANDOM ACCESS MEMORY DEVICE AND ITS METHOD OFMANUFACTURE, having the same inventors of Richard Lienau and LaurenceSadwick.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to nonvolatile random access magneticmemory devices. More particularly, the present invention relates to animproved Hall effect ferromagnetic random access memory cell and itsmethod of fabrication.

2. State of the Art

The Hall effect is an electromagnetic phenomenon whereby a conductorcarrying an electric current perpendicular to an applied magnetic fielddevelops a voltage gradient which is transverse to both the current andthe magnetic field. This principle has been applied in manyelectromagnetic devices, including those constructed with semiconductingmaterials to produce field effect transistors (FETs).

FETs are well known and have been used to create digital memory devices.For example, U.S. Pat. No. 5,295,097 to Lienau teaches a Hall effectmemory device comprising a domain made of ferromagnetic material,substantially surrounded by a conducting coil. When the coil is suppliedwith an electric current, a residual magnetic field is created in thedomain, the polarity of this magnetic field depending on the directionof the current of the coil. This is how digital information is writtento the domain. A FET is disposed so as to be perpendicularly penetratedby this field, the differential voltage across the drains of the FETindicating the polarity of the magnetic field. This is how digitalinformation is read from the domain.

While these devices are known in the art, they are somewhat difficultand costly to construct. Additionally, fabrication constraints affectthe density of placement of the devices on a computer chip, and thusaffect the overall size of digital computer components. It would bedesirable to have a hall effect ferromagnetic random access memorydevice that is less expensive and less difficult to fabricate, and whichis also smaller and may be disposed on a microchip in greater density.

OBJECTS AND SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a Halleffect ferromagnetic random access memory cell that is easier and lessexpensive to mass produce than other such devices.

It is another object of the invention to provide a Hall effectferromagnetic random access memory cell that provides better signalsensing capabilities than other such devices.

It is another object of the invention to provide a method of massproducing such cells that is easier and less expensive to mass producethan prior devices.

It is yet another object of the invention to provide a random accessmemory circuit that is comprised of a matrix of Hall effectferromagnetic random access memory cells constructed according to thisinvention.

It is another object of the invention to provide Hall effectferromagnetic random access memory cells that are reproducible in theirbehavior and give a high yield.

The above and other objects are realized in a method of manufacturing aHall effect ferromagnetic non-volatile random access memory cellcomprising the steps of providing a piece of substrate material;depositing upon the surface of the substrate a Hall sensor material;depositing upon the surface of the substrate interconnect lines forelectrically connecting the Hall sensor material to its source anddrains; depositing upon the Hall sensor material and the interconnectlines a first layer of insulating material; depositing upon the firstlayer of insulating material a thin layer of ferromagnetic material;depositing an additional desired thickness of ferromagnetic materialupon the thin layer of ferromagnetic material; forming the ferromagneticmaterial into a magnetically polarizable domain having a long axissubstantially perpendicular or normal to the plane of the substrate;depositing upon the ferromagnetic material a second layer of insulatingmaterial; depositing upon the second layer of insulating material a thinlayer of electrically conductive material by means of electron beamdeposition, sputtering, or other thin film deposition technique;depositing on the thin layer of electrically conductive material anadditional desired thickness of electrically conductive material by theprocess of electroplating; forming the electrically conductive materialinto a coil substantially surrounding the length of the domain andconfigured to produce a residual magnetic field therein when anelectrical current is applied to the coil; depositing upon the surfaceof the electrically conductive material and the second layer ofinsulating material interconnect lines for uniquely electricallyconnecting the coil to a bit write line and a word write line; andcoating the entire cell structure with a passivation layer.

These and other objects are also realized in a Hall effect ferromagneticnon-volatile random access memory apparatus comprising a substratehaving a plurality of elongate, magnetically polarizable domainsoriented with their long axis substantially normal to the substrate. Aplurality of word write lines and bit write lines are also carried bythe substrate, and a plurality of conductive coil members are connectedthereto, each between one of the word write lines and one of the bitwrite lines and substantially surrounding and being coupled to one ofthe domains and having a central axis oriented substantially parallel tothe long axis of the domains. A current source is connected to the wordwrite lines and bit write lines for driving a current through a selectedcoil member so as to switch the residual magnetic field direction of thedomain coupled thereto, and at least one magnetic field sensor islocated proximate to each domain for passively sensing the direction ofthe residual magnetic field of that domain.

Some of the above objects are also realized in a Hall effectferromagnetic non-volatile random access memory apparatus describedabove wherein the sensors comprise a field effect transistor defining aHall effect channel connected to a pair of drains and oriented forsubstantially perpendicular penetration of its channel by the residualmagnetic field of the adjacent domain. The memory apparatus also has aplurality of word read lines and bit read lines carried by thesubstrate, and each of the field effect transistors are uniquelyconnected with its source to one of the word read lines and each of itsdrains to one of the bit read lines. A current source is provided forselectively supplying a current to each of the word read lines. Acomparator for comparing the voltage across each of the paired bit readlines is provided to determine the memory status of the domain.

Other objects and features of the present invention will be apparent tothose skilled in the art, based on the following description, taken incombination with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a lateral cross section through a Hall EffectFerromagnetic Random Access Memory (HFRAM) cell according to the presentinvention.

FIG. 2 provides a lateral cross section through an alternativeembodiment of an HFRAM cell according to the present invention in whichthe ferromagnetic bit lies directly atop the sensor.

FIG. 3 provides a top sectional view of a HFRAM cell according to thepresent invention.

FIG. 4 provides a top view of an alternative embodiment of the sensorand conductor arrangement for an HFRAM cell according to the presentinvention.

FIG. 5 provides a lateral cross section through an alternativeembodiment of the HFRAM cell of the present invention in which theconductors overlie rather than abut the sensor.

FIG. 6 provides a lateral cross section through an alternativeembodiment of the HFRAM cell of the present invention wherein theconductors overlie rather than abut the sensor, and the ferromagneticbit lies directly atop the sensor.

FIG. 7 provides a lateral cross section through the HFRAM cell of FIG. 1showing a via emanating from the right side of the coil.

FIG. 8 is a schematic diagram of a typical write, or storage drive,matrix layout interconnecting an array of HFRAM memory cells accordingto the present invention.

FIG. 9 provides a schematic diagram of a typical read, or sense drive,matrix layout interconnecting an array of HFRAM memory cells accordingto the present invention.

FIG. 10 provides a lateral cross section through an alternativeembodiment of the HFRAM cell of the present invention wherein theferromagnetic bit is disposed directly on the substrate and the sensoris disposed directly over the ferromagnetic bit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings:

FIG. 1 provides a lateral cross section through a Hall EffectFerromagnetic Random Access Memory (HFRAM) cell according to the presentinvention. This sectional view is taken through section 1-1 of FIG. 3,which provides a top sectional view of the same HFRAM cell. Beginning atthe bottom of FIG. 1, the chip is formed on a substrate material 8preferably comprised of glass, silicon (Si), gallium arsenide (GaAs) orother suitable material known in the art. In one embodiment of thepresent invention, the substrate 8 may comprise a layer of finishedintegrated circuitry devices, thus providing greater component densitythan other devices.

Immediately atop the substrate 8 is a Hall effect sensor 2, which istypically connected to four conductors 4 (two of which are visible inthe sectional view of FIG. 1) which connect the sensor to the sense, orread, matrix. Above the layer containing the sensor 2 and conductors 4is a layer of insulating material 5. This insulating material ispreferably silicon nitride (Si₃N₄) or silicon dioxide (SiO₂), but othersuitable insulating materials known in the art may be used. Theinsulating material 5 separates the sense conductors 4 from the write,or storage drive coil 3, shown in cross-section in this view.

The storage drive coil 3 wraps around the ferromagnetic bit 1, with anintervening layer of insulating material 6 disposed therebetween. Theferromagnetic bit 1 is preferably formed of a ferromagnetic materialselected from the group comprising iron, cobalt, nickel, gadolinium,indium arsenide, silicon, gallium arsenide, and indium antimonide. Othermaterials known in the art may also be suitable in accordance with theprinciples of this invention. The ferromagnetic bit is preferablyoriented with its long axis approximately perpendicular to the plane ofthe Hall effect sensor (and, in this embodiment, the plane of thesubstrate), so as to create a proper magnetic flux. The ratio of thelength of the domain to its width in the plane of the substrate shouldbe greater than 1:1, with a ratio of 2:1 or greater being preferable.The coil is formed of a conducting material, such as silver, copper,gold, aluminum, or other conductive material known in the art. Theinsulating material 6 is preferably silicon nitride (Si₃N₄) or silicondioxide (SiO₂), but other suitable insulating materials known in the artmay be used. The entire cell structure is overlain by an insulatingcover 7, preferably made of silicon dioxide (SiO₂) or silicon nitride(Si₃N₄), though other materials known in the art may be advantageouslyused.

The wrapped configuration of the storage drive coil 3 around theferromagnetic bit 1 is more clearly shown in FIG. 3, which is a topsectional view of the HFRAM cell taken through section 3—3 of FIG.7. Inthis view, the coil 3 is shown overlying the bit drive white line 10 onone end, and having a via 9 extending out from the plane of the figureon its other end. The coil 3 is electrically connected at the one end tothe drive write line 10, and the via 9 connects the other end of thecoil 3 to the byte drive line 15, shown more clearly in the schematicdiagram of FIG. 8. The configuration of the bit and byte drive lines, 10and 15, are shown for reference only, and in practice may be reversedfrom the orientation shown.

FIG. 2 provides a lateral cross section through an alternativeembodiment of an HFRAM cell according to the present invention. The cellof this embodiment is identical to that of FIG. 1 except that theinsulating layer 5 is absent, and the ferromagnetic bit 1 lies directlyatop the sensor 2. This configuration is possible because, although theferromagnetic material of the bit is conductive, it is isolated from thestorage, or write, drive circuit 3 by the insulator 6, and thuselectrically is not part of the write drive circuit. In the depiction ofFIG. 2 the insulator 6 is shown extended below the coil 3, thuselectrically isolating the write drive and read sense circuits. Thisconfiguration provides the advantage of having the sensor 2 closer tothe bit 1, which enhances the signal-to-noise ratio because the sensoris placed in the most intense part of the magnetic field.

FIG. 4 provides a top view of an alternative embodiment of the sensorand conductor arrangement for an HFRAM cell according to the presentinvention. This view is taken through section 4—4 of FIG. 5. Thisembodiment is a “classic” Hall effect device, in which the Hallconductor region is comprised of indium antimonide (InSb), indiumarsenide (InAs), gallium arsenide (GaAs), silicon (Si), or otherappropriate Hall effect coefficient material. Other forms of sensors mayalso be used, including those which create variations of the Halleffect, but in all cases the sensing device must be capable ofdetermining the direction or polarity of the magnetic field emanatingfrom the ferromagnetic bit 1. In FIG. 4, the four conductors 4 are shownoverlapping the edge of the sensor 2, having a top connection, ratherthan butt connection as depicted in FIGS. 1, 2, & 7. A side view of thistype of configuration is given in FIG. 5. This configuration reduces theoverall thickness of the device, and thereby increases the allowabledensity of these devices on a semiconductor ship. In FIG. 4, two of thefour conductors 4 are shown with vias 12, depicted in such a way as toindicate that they are extending out of the plane of the drawiung. Theseare in turn connected to the read sense comparator lines 19 (FIG. 9).

FIG. 5 provides a lateral cross section through another alternativeembodiment of the HFRAM cell of the present invention in which theconductors 4 overlie rather than abut the sensor 2. As noted above, thisconfiguration also provides manufacturing simplicity and costadvantages, and increases the allowable density of components on asemiconductor chip. The view of FIG. 5 is taken through section 5—5 ofFIG. 4. In this embodiment, the sensor 2 is approximately twice as largeas its counterpart in FIGS. 1 or 2, and the sense conductors 4 contactthe sensor 2 on its top as in FIG. 4, rather than butting against it asin FIGS. 1, 2 & 7. The embodiment of FIG. 5 also includes an insulatinglayer between the sensor and the bit 1, however, this insulator 5 isconfigured to conform to the rise caused by the sense conductors 4. Thisrise may also cause a gap 11 between the under surface of the conductors4 and the edge of the sensor 2, which is preferably filled with aninsulating material such as silicon nitride (Si₃N₄), or other suitableinsulating material known in the art.

The unique features of the embodiments of FIG. 2 and FIG. 5 may beadvantageously combined to provide an HFRAM cell having all of thoseadvantages. FIG. 6 provides a lateral cross section through analternative embodiment of the HFRAM cell of the present inventionincorporating these features. The conductors 4 overlie rather than abutthe sensor 2, and the ferromagnetic bit 1 lies directly atop the sensor2. The principle advantages of this configuration are that it increasessensor sensitivity, and makes the manufacturing process simpler and lesscostly.

FIG. 7 provides a lateral cross section through the HFRAM cell of FIG. 1showing a via 9 emanating from the right side of the coil 3. As notedabove, the via 9 connects one end of the coil 3 to the byte drive line15. The byte drive line 15 is shown more clearly in FIG. 8, whichprovides a schematic diagram of a typical write, or storage drive,matrix layout interconnecting an array of HFRAM memory cells accordingto the present invention. The matrix is in a typical 8-bit byteconfiguration, with bits b₀ through b₇ and bytes B₀ through B_(n). Itwill be apparent to one skilled in the art that this configuration istypical of computer memory devices. However, the present invention is inno way limited to devices configured in this manner. The ferromagneticbits 1 are shown centered in reference to the write drive coils (orloops) 3. Each cell coil or loop 3 is interconnected electrically to thewrite drive matrix through the bit drive lines 10 and the vias 9 to thebyte drive lines 15. The bit drive circuitry is represented in thisfigure by objects 14, and the byte drive circuits are represented byobjects 13. Objects 21 represent individual bit matrix select circuitry,which may be constructed in any suitable manner known in the art.

FIG. 9 provides a schematic diagram of a typical read, or sense drive,matrix layout interconnecting an array of HFRAM memory cells accordingto the present invention. As above, this matrix is also in a typical8-bit byte configuration, with bits b₀ through b₇ and bytes B₀ throughB_(n). In this depiction, the sensors are “classic” Hall effect sensors,as noted in the discussion of FIG. 4 above, but the invention heredescribed is not restricted to such. The ferromagnetic bits 1 arecentered with respect to the sensors 2, and may be disposed over thesensors as heretofore depicted, or disposed under the sensors asdepicted in FIG. 10 (described in more detail below). Each sensor iselectrically interconnected to the read drive matrix through senseconnectors 4. The byte row drive select lines 18 connect to each sensorin a row through a connector 4. When a given byte row is selected,current flows from the byte selection and drive circuit 17 through theline 18, the sensor 2, and thence to the common ground 20 through amatching sensor conductor 4. In this case, the Hall voltage developedacross the sensor as a result of the current applied across the sensor 2by the byte drive current and biased by the magnetic field emanatingfrom the ferromagnetic bit 1 is transmitted through the second set ofsensor connectors 4 and the vias 12 to the sense lines 19 and thence tothe bit sense comparators 16, b₀ through b₇. Line 20 connects each cellto ground.

FIG. 10 provides a lateral cross section through an alternativeembodiment of the HFRAM cell of the present invention wherein theferromagnetic bit 1 is disposed directly on the substrate 8, and thesensor 2 is disposed directly above the ferromagnetic bit, rather thanunder it as in previous depictions. All other feature relationshipsremain the same as in FIGS. 1, 2, 5, 6, and 7. As will be apparent toone skilled in the art, the memory cells of the present invention may bedeposed over other integrated circuitry, such as other layers of HFRAMcells, transistors, etc., such as in a processor chip, or othercircuitry requiring non-volatile RAM.

The HFRAM cell of this invention is advantageously manufactured in thefollowing manner. First, a piece of substantially planar substratematerial is provided. This substrate material is preferably a conductivematerial. Next, a layer of insulating material is deposited upon thesurface of the substrate. This step must be performed before the Hallsensor material is deposited. Upon the surface of the insulatingmaterial and substrate, a Hall sensor material is deposited. The Hallsensor material may be indium antimonide (InSb), gadolinium, manganese,or other suitable materials. Next, interconnect lines for electricallyconnecting the Hall sensor material to its source and drains aredeposited upon the surface of the substrate wafer, and then a firstlayer of insulating material is deposited upon the Hall sensor materialand the interconnect lines.

At this point, the ferromagnetic domain must be formed on the substrate.To do so, first, a thin layer of ferromagnetic material is depositedupon the layer of insulating material mentioned above. Suitablematerials for forming the domain include but are not limited to iron,cobalt, nickel, gadolinium, indium arsenide, silicon, gallium arsenide,and indium antimonide. The domain may be deposited on the substrate byany suitable thin film deposition process, such as electroplating,sputtering, electron beam deposition, chemical vapor deposition, orothers known in the art. Then, an additional desired thickness offerromagnetic material is deposited on this thin layer by the sameprocess, until a ferromagnetic domain of suitable mass is created. Thisferromagnetic material is then shaped and formed into a magneticallypolarizable domain having a long axis substantially perpendicular to theplane of the substrate, so as to retain a residual magnetic field with amagnetic flux in a desired direction exposed to an electrical field bythe drive coil. A second layer of insulating material is then depositedupon the ferromagnetic domain material, and the device is ready for theapplication of the drive coil.

The drive coil must be formed to substantially surround the long axis ofthe Hall sensor material. It is created in the following manner. First,a thin layer of electrically conductive material is deposited upon thesecond layer of insulating material mentioned above. This may be done bymeans of electron beam deposition or other suitable thin film depositiontechniques. An appropriate material for forming this coil is anyelectrically conductive material, preferably a metal such as copper,silver, aluminum, or gold. After the thin layer of conductive materialis in place, an additional desired thickness of electrically conductivematerial is deposited on this thin layer by electroplating or some othersimilar thin film deposition process to obtain a sufficient mass ofconducting coil material. As with the ferromagnetic domain, theelectrically conductive material must be formed into a coilsubstantially surrounding the length of the domain, so as to beconfigured to produce a residual magnetic field in the domain when anelectrical current is applied to the coil.

After the domain and coil are completed, interconnect lines for uniquelyelectrically connecting the coil to a bit write line and a word writeline are deposited upon the surface of the electrically conductivematerial and the second layer of insulating material. To complete thecell, the entire cell structure is coated with a passivation layer asmentioned above.

After the above steps are completed, the electrical function of the cellstructure is preferably tested to determine whether it functionsproperly, and the substrate material is cut into an appropriate size andshape for bonding each individual cell to a header. In this way, aplurality of cells as described herein may be interconnected to form arandom access memory matrix as described above.

It is to be understood that the above-described arrangements are onlyillustrative of the application of the principles of the presentinvention. Numerous modifications and alternative arrangements may bedevised by those skilled in the art without departing from the spiritand scope of the present invention and the appended claims are intendedto cover such modifications and arrangements.

What is claimed is:
 1. A Hall effect ferromagnetic non-volatile randomaccess memory device comprising: a) a substantially planar substrate; b)a separate magnetically polarizable elongate domain carried by saidsubstrate and having a height to width aspect ratio of greater than 1:1;c) a word write line positioned on said substrate; d) a bit write linepositioned on said substrate; e) a conductive coil positioned on saidsubstrate, the coil member substantially surrounding and being coupledto the domain and having a central axis representing a center of a loop,said central axis being oriented substantially parallel to a long axisof the domain, the coil uniquely connected between the word write lineand the bit write line; f) means connected to said word write line andsaid bit write line for driving a current through the coil of sufficientmagnitude to switch the residual magnetic field direction of the domain;and g) a magnetic field sensor disposed adjacent to an end of the domainopposite the substrate for passively sensing the direction of theresidual magnetic field of the domain.
 2. The memory device of claim 1wherein said sensor comprises a field effect transistor defining a Halleffect channel connected to a pair of drains and oriented forsubstantially perpendicular penetration of its channel by the residualmagnetic field of a different domain, said field effect transistor alsocomprising a gate controlling majority carrier flow through its channel,said memory further comprising: a) a word read line carried by saidsubstrate; b) a paired bit read line carried by said substrate; c) thefield effect transistor uniquely connected with its source to said wordread lines and the drains to said paired bit read line; d) means forselectively supplying a current to said word read line; and e) means forcomparing the voltage across said paired bit read line.
 3. The devicedescribed in claim 2 wherein the domain is formed from a ferromagneticmaterial selected from the group comprising iron, cobalt, nickel,gadolinium, indium arsenide, silicon, gallium arsenide, and indiumantimonide.
 4. The device described in claim 3 wherein the ferromagneticmaterial is doped with a non-ferrous material selected from the groupconsisting of aluminum, barium, boron, copper, chromium, molybdenum, andvanadium.
 5. The device described in claim 3 wherein the domain isdeposited upon the substrate by a method selected from the groupcomprising electroplating, sputtering, electron beam deposition, andchemical vapor deposition.
 6. A ferromagnetic non-volatile RAM device asdescribed in claim 2 wherein the sensor is disposed between thesubstrate and the domain, and the domain is deposited directly upon thesensor.
 7. A ferromagnetic non-volatile RAM device as described in claim3 wherein the domain is deposited directly on a passivated substrateselected from the group comprising silicon, gallium arsenide, quartz,and glass.
 8. A ferromagnetic non-volatile RAM device as described inclaim 3 wherein the memory device is deposited directly over otherfinished integrated circuitry devices on the same substrate.
 9. A Halleffect ferromagnetic non-volatile random access memory devicecomprising: a) a substantially planar substrate; b) a separatemagnetically polarizable elonoate domain carried by said substrate andhaving a height to width aspect ratio of greater than 1:1; c) a wordwrite line positioned on said substrate; d) a bit write line positionedon said substrate; e) a conductive coil positioned on said substrate,the coil member substantially surrounding and being coupled to thedomain and having a central axis representing a center of a loop, saidcentral axis being oriented substantially parallel to a long axis of thedomain, the coil uniquely connected between the word write line and thebit write line; f) means connected to said word write line and said bitwrite line for driving a current through the coil of sufficientmagnitude to switch the residual magnetic field direction of the domain;and g) a magnetic field sensor disposed between the domain and thesubstrate for passively sensing the direction of the residual magneticfield of that domain.
 10. The memory device of claim 9 wherein saidsensor comprises a field effect transistor defining a Hall effectchannel connected to a pair of drains and oriented for substantiallyperpendicular penetration of its channel by the residual magnetic fieldof a different domain, said field effect transistors also comprising agate controlling majority carrier flow through its channel, said memoryfurther comprising: a) a word read line carried by said substrate; b) apaired bit read line carried by said substrate; c) said field effecttransistor uniquely connected with its source to said word read line andits drains to said paired bit read line; d) means for selectivelysupplying a current to said word read line; and e) means for comparingthe voltage across said paired bit read line.
 11. The device describedin claim 10 wherein the domain is formed from a ferromagnetic materialselected from the group comprising iron, cobalt, nickel, gadolinium,indium arsenide, silicon, gallium arsenide, and indium antimonide. 12.The device described in claim 11 wherein the ferromagnetic material isdoped with a non-ferrous material selected from the group consisting ofaluminum, barium, boron, copper, chromium, molybdenum, and vanadium. 13.The device described in claim 11 wherein the domain is deposited uponthe substrate by a method selected from the group comprisingelectroplating, sputtering, electron beam deposition, and chemical vapordeposition.
 14. A ferromagnetic non-volatile RAM device as described inclaim 10 wherein the sensor is disposed between the substrate and thedomain, and the domain is deposited directly upon the sensor.
 15. Aferromagnetic non-volatile RAM device as described in claim 11 whereinthe domain is deposited directly on a passivated substrate selected fromthe group comprising silicon, gallium arsenide, quartz, and glass.
 16. Aferromagnetic non-volatile RAM device as described in claim 11 whereinthe memory device is deposited directly over other finished integratedcircuitry devices on the same substrate.
 17. A Hall effect ferromagneticnon-volatile random access memory device comprising: a) a substantiallyplanar substrate; b) a separate magnetically polarizable elongate domaincarried by said substrate and having a height to width aspect ratio ofgreater than 1:1; c) a word write line positioned on said substrate; d)a bit write line positioned on said substrate; e) a conductive coilpositioned on said substrate, the coil member substantially surroundingand being coupled to the domain and having a central axis representing acenter of a loop, said central axis being oriented substantiallyparallel to a long axis of the domain, the coil uniquely connectedbetween the word write line and the bit write line; f) means connectedto said word write line and said bit write line for driving a currentthrough the coil of sufficient magnitude to switch the residual magneticfield direction of the domain; and g) two magnetic field sensorsdisposed proximate the domain, a first sensor being disposed between thedomain and the substrate, and a second sensor being disposed adjacentthe domain opposite the substrate, for passively sensing the directionof the residual magnetic field of the domain.
 18. The memory device ofclaim 17 wherein said sensor comprises a field effect transistordefining a Hall effect channel connected to a pair of drains andoriented for substantially perpendicular penetration of its channel bythe residual magnetic field of a different domain, said field effecttransistor also comprising a gate controlling majority carrier flowthrough its channel, said memory further comprising: a) a word read linecarried by said substrate; b) a paired bit read line carried by saidsubstrate; c) said field effect transistor uniquely connected with itssource to said word read line and its drains to said paired bit readline; d) means for selectively supplying a current to said word readline; and e) means for comparing the voltage across said paired bit readline.
 19. The device described in claim 18 wherein the domain is formedfrom a ferromagnetic material selected from the group comprising iron,cobalt, nickel, gadolinium, indium arsenide, silicon, gallium arsenide,and indium antimonide.
 20. The device described in claim 19 wherein theferromagnetic material is doped with a non-ferrous material selectedfrom the group consisting of aluminum, barium, boron, copper, chromium,molybdenum, and vanadium.
 21. The device described in claim 19 whereinthe domain is deposited upon the substrate by a method selected from thegroup comprising electroplating, sputtering, electron beam deposition,and chemical vapor deposition.
 22. A ferromagnetic non-volatile RAMdevice as described in claim 18 wherein the sensor is disposed betweenthe substrate and the domain, and the domain is deposited directly uponthe sensor.
 23. A ferromagnetic non-volatile RAM device as described inclaim 19 wherein the domain is deposited directly on a passivatedsubstrate selected from the group comprising silicon, gallium arsenide,quartz, and glass.
 24. A ferromagnetic non-volatile RAM device asdescribed in claim 19 wherein the memory device is deposited directlyover other finished integrated circuitry devices on the same substrate.